# Explain The Meaning Of Topology Computer Science Essay

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Computer networking or Data communications Datacom is the engineering discipline concerned with the communication between computer systems or devices. A computer network is any set of computers or devices connected to each other with the ability to exchange data. Computer networking is sometimes considered a sub-discipline oftener communications, computer science, information technology and/or computer engineering since it relies heavily upon the theoretical and practical application of these scientific and engineering disciplines. The three types of networks are: the Internet, the intranet, and the extranet. Users and network administrators typically have different views of their networks. Users can share printers and some servers from a workgroup, which usually means they are in the same geographic location and are on the same LAN. Before the advent of computer networks that were based upon some type of telecommunications system, communication between calculation machines and early computers was performed by human users by carrying instructions between them. Many of the social behaviors seen in today's Internet were demonstrably present in the nineteenth century and arguably in even earlier networks using visual signals.

A group of business employees would like to set up a small networking office. Explain the meaning of topology. Discuss and draw the different types of network topology that are available.

Topology is a branch of mathematics. It studies the properties of objects that do not change when the object is distorted. In topology two objects are considered to be the same if each one can be distorted to the other without being cut or torn.

There are everyday examples of topology. A typical map of a railway system shows the railway lines and how they connect in very simple form. An accurate map of a railway system would have lots of bends and uneven spacing. The simplified map is topologically equivalent to an accurate map. The important information, like the order of stops and how the different train lines are connected, does not change as the map is distorted from one to the other.

Topology can be considered as a virtual shape or structure of a network. This shape does not correspond to the actual physical design of the devices on the computer network. The computers on a home network can be arranged in a circle but it does not necessarily mean that it represents a ring topology.

Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. The study of network topology uses graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.

A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN has one or more links to one or more nodes in the network and the mapping of these links and nodes in a graph results in a geometric shape that may be used to describe the physical topology of the network. Likewise, the mapping of the data flow between the nodes in the network determines the logical topology of the network. The physical and logical topologies may or may not be identical in any particular network. Types of network topology Bus TopologyÃ¯Â¼Å’Star Topology, Ring Topology, Tree Topology, Mesh Topology, Hybrid Topology.

## Bus topology

http://www.computerhope.com/jargon/b/bustopol.gif

In local area networks where bus topology is used, each machine is connected to a single cable. Each computer or server is connected to the single bus cable through some kind of connector. A terminator is required at each end of the bus cable to prevent the signal from bouncing back and forth on the bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the MAC address or IP address on the network that is the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data does match the machine address, the data is accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable breaks, the entire network will be down.

## STAR TOPOLOGY

http://www.escotal.com/Images/Network%20parts/topology_star.gif

In local area networks with a star topology, each network host is connected to a central hub. In contrast to the bus topology, the star topology connects each node to the hub with a point-to-point connection. All traffic that traverses the network passes through the central hub. The hub acts as a signal booster or repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.

## RING TOPOLOGY

http://www.computerhope.com/jargon/r/ring.gif

In local area networks where the ring topology is used, each computer is connected to the network in a closed loop or ring. Each machine or computer has a unique address that is used for identification purposes. The signal passes through each machine or computer connected to the ring in one direction. Ring topologies typically utilize a token passing scheme, used to control access to the network. By utilizing this scheme, only one machine can transmit on the network at a time. The machines or computers connected to the ring act as signal boosters or repeaters which strengthen the signals that traverse the network. The primary disadvantage of ring topology is the failure of one machine will cause the entire network to fail.

## TREE TOPOLOGY

http://www.computerhope.com/jargon/t/tree.gif

The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node that has no other node above it in the hierarchy (The hierarchy of the tree is symmetrical.) Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy, the number, being referred to as the 'branching factor' of the hierarchical tree.This tree has individual peripheral nodes.

## MESH TOPOLOGY

http://www.computerhope.com/jargon/m/mesh.gif

The type of network topology in which some of the nodes of the network are connected to more than one other node in the network with a point-to-point link this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network.

## HYBRID TOPOLOGY

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Hybrid topology composed of a combination of two or more basic topologies. These network mappings aim at harnessing the advantages of each of the basic topologies used in them. Network topologies are the physical arrangements of network nodes and wires. All of them I list it is the different type of topology. Each of them are different usage in networking.

## QUESTION 2

The purpose of data link control is to provide functions like flow control, error detection and error control. Explain each function in detail.

DLC (data link control) is the service provided by the data link layer of function defined in the Open Systems Interconnection model for network communication. The Data Link layer is responsible for providing reliable data transfer across one physical link (or telecommunications path) within the network. Some of its primary functions include defining frames, performing error detection or ECC on those frames, and performing flow control (to prevent a fast sender from overwhelming a slow receiver).

Many point-to-point protocols exist at the Data Link layer including High-level Data Link Control (HDLC), Synchronous Data Link Control (SDLC), Link Access Procedure Balanced (LAPB), and Advanced Data Communications Control Procedure (ADCCP). All of these protocols are very similar in nature and are found in older networks. In the Internet, one of two point-to-point protocols are used at this layer: Serial Line Internet Protocol (SLIP) or Point-to-Point Protocol (PPP) with PPP being the newer, approved standard. All of these protocols are used in point-to-point connections such as those on metropolitan area network (MAN) or wide area network (WAN) backbones or when we dial our Internet service provider (ISP) from home using a modem.

In local area networks (LANs) where connections are multipoint rather than point-to-point and require more line-sharing management, the Data Link layer is divided into two sublayers: the Logical Link Control layer and the Media Access Control layer. The Logical Link Control layer protocol performs many of the same functions as the point-to-point data link control protocols described above. The Media Access Control (MAC) layer protocols support methods of sharing the line among a number of computers. Among the most widely used MAC protocols are Ethernet, Token Bus, and Token Ring and their derivatives.

In data communications, flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with data from transmitting node. Flow control should be distinguished from congestion control, which is used for controlling the flow of data when congestion has actually occurred. Flow control mechanisms can be classified by whether or not the receiving node sends feedback to the sending node.

Flow control is important because it is possible for a sending computer to transmit information at a faster rate than the destination computer can receive and process them. This can happen if the receiving computers have a heavy traffic load in comparison to the sending computer, or if the receiving computer has less processing power than the sending computer.

Error detection is most commonly realized using a suitable hash function . A hash function adds a fixed-length tag to a message, which enables receivers to verify the delivered message by recomputing the tag and comparing it with the one provided.

There exists a vast variety of different hash function designs. However, some are of particularly widespread use because of either their simplicity or their suitability for detecting certain kinds of errors e.g., the cyclic redundancy check's performance in detecting burst errors.

Random-error-correcting codes based on minimum distance coding can provide a suitable alternative to hash functions when a strict guarantee on the minimum number of errors to be detected is desired. Repetition codes, described below, are special cases of error-correcting codes: although rather inefficient, they find applications for both error correction and detection due to their simplicity.

Error control is a method that can be used to recover the corrupted data whenever possible. There are two basic types of error control which are backward error control and forward error control. In backward error control, the data is encoded so that the encoded data contains additional redundant information which is used to detect the corrupted blocks of data that must be resent. On the contrary, in forward error control (FEQ), the data is encoded so that it contains enough redundant information to recover from some communications errors.

## CONCLUSION

After doing data communication and networking assignment, I know many about datacom knowledge such as meaning of topology and different type of topology. In Computer Networking topology refers to the layout or design of the connected devices. Network Topologies can be physical or logical. In this section I will illustrate on the different types of the topologies. There are bus topology, ring topology, mesh topology, star topology and other. All of it has different usage in network topology. In question 2, I can know about the purpose of data link control is to provide functions like flow control, error detection and error control. All of that are very useful to me when I working to be a successful people.